1. Field of the Invention
The present invention relates to a precharge system for an active matrix display device, which is integrated on the display peripheral area and comprises low temperature poly-silicon (LTPS) thin film transistors. Before data is written onto a data line, a precharge voltage is input into the data line to raise voltage to a predetermined level, thus accelerating the reaction of a liquid crystal display (LCD) unit.
2. Description of the Related Art
FIG. 1 is a schematic diagram showing a conventional LCD device with integrated driving circuits on display peripheral area. FIG. 2 is a plot showing a clock timing of the conventional LCD device. As shown in FIG. 1, a vertical driving circuit V driver 1 synchronizes a vertical start signal VST, with a vertical clock signal VCK, to provide vertical scan signals ΦV1, ΦV2, ΦV3, ΦVM for selecting gate lines X. During a frame, a horizontal driving circuit H driver 2 provides each signal line Y with a video signal VSIG sequentially. Therefore, video data is written into the LCD device by a dot matrix scanning method. A terminal of each signal line Y has a horizontal switch (HSW1, HSW2, HSW3, . . . , HSWN) and is thereby coupled to a video signal line 3. The horizontal driving circuit H driver 2 synchronizes a horizontal start signal HST, according to a horizontal clock signal HCK, to provide sample impulse signals ΦH1, ΦH2, ΦH3, . . . , ΦHN for controlling the corresponding horizontal switches to sample and retain video signals from the signal lines Y.
When sampling the video signal VSIG, a precharge circuit 4 provides each signal line Y with a precharge signal VPS. The precharge circuit 4 is coupled to a terminal of each signal line Y through precharge switches PSW1, PSW2, PSW3, and PSW4. A control circuit P driver 5 controls the precharge switches PSW to turn on or off and provides each signal line Y with the precharge signal VPS. The control circuit D driver 5 synchronizes a precharge start signal PST, with a precharge clock signal PCK, to provide the precharge switches PSW with precharge sample impulse signals ΦP1, ΦP2, ΦP3, . . . , ΦPN.
The conventional LCD device requires an additional precharge signal VPS to provide voltage required by a gray scale LCD pixel on the signal line.